Changing device a rented movie can be played on?

I rented a movie on a windows PC, it wouldn't play there so I decided to watch it on my mac. I deauthorised the windows PC from my account and the movie is no longer shown on that PC. Now trying to play the movie on my mac, it says it is authorised to play on another device. When I initially tried to play the movie on the windows PC it never got past contacting the itunes store and kept giving me an error message, each time asking if I was sure I wanted to play as I would have 48 hours from that point to watch, so surely the movie was never authorised on that computer to play anyway?